Medical camera

ABSTRACT

A medical camera includes a camera head having a first a first color separation prism, a second color separation prism, a third color separation prism, and a fourth color separation prism. The four color separation prisms respectively separate light incident from an affected area into a blue, red and green color components, and an infrared (IR) component. A light emission surface of the first color separation prism is disposed opposite to a light emission surface of the second color separation prism. A light emission surface of the third color separation prism is disposed across an incident ray which is incident vertically to an object side incident surface of the first color separation prism.

CROSS REFERENCES TO RELATED APPLICATIONS

This Application is a continuation application of the pending U.S.patent application Ser. No. 16/230,002, filed on Dec. 21, 2018, which isa continuation application of U.S. patent application Ser. No.16/155,233, filed on Oct. 9, 2018, which is a continuation applicationof U.S. patent application Ser. No. 15/480,849, filed on Apr. 6, 2017,now U.S. Pat. No. 10,122,975, issued on Nov. 6, 2018, which claimspriority from Japanese Patent Application No. 2016-184797, filed on Sep.21, 2016, and No. 2016-100738, filed on May 19, 2016, the contents ofwhich are hereby incorporated by reference in their entireties.

BACKGROUND 1. Technical Field

The present disclosure relates to an endoscope and an endoscope system.

2. Description of the Related Art

In the related art, an endoscope system using a three color separationprism is known. For example, Japanese Patent Unexamined Publication No.2013-116357 discloses the endoscope system. The endoscope systemacquires a captured color image on which a specific area in a body isexpressed in combination with three colors of R (red color), G (greencolor), and B (blue color), and performs image processing on thecaptured image in order to emphasize a designated wavelength component.

According to the endoscope system disclosed in Japanese PatentUnexamined Publication No. 2013-116357, if an IR light (infrared light)component is added to the image in addition to the three colors of RGB,the image captured by an endoscope shows insufficient image quality.

SUMMARY

The present disclosure is made in view of the above-describedcircumstances, and aims to provide an endoscope and an endoscope systemwhich can improve image quality by adding an infrared light component toan image.

An endoscope according to the present disclosure includes a four colorseparation prism that includes a first color separation prism, a secondcolor separation prism, a third color separation prism, and a fourthcolor separation prism which respectively separate light incident froman affected area into a first color component, a second color component,a third color component, and a fourth color component which are any oneof a blue color component, a red color component, a green colorcomponent, and an IR component, a first color image sensor that isinstalled in the first color separation prism, and that converts theseparated first color component into an electric signal, a second colorimage sensor that is installed in the second color separation prism, andthat converts the separated second color component into an electricsignal, a third color image sensor that is installed in the third colorseparation prism, and that converts the separated third color componentinto an electric signal, a fourth color image sensor that is installedin the fourth color separation prism, and that converts the separatedfourth color component into an electric signal, and a signal output thatoutputs a color image signal and an IR signal from the respectivelyconverted electric signals. The first color separation prism, the secondcolor separation prism, the third color separation prism, and the fourthcolor separation prism are sequentially disposed from an object sidewhen receiving the light incident from the affected area. The firstcolor image sensor is disposed opposite to the second color image sensorand the third color image sensor across an incident ray which isincident vertically to an object side incident surface of the firstcolor separation prism.

According to the present disclosure, it is possible to improve imagequality of an image captured by an endoscope by adding an infrared lightcomponent to the captured image.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating an external configuration of anendoscope according to a first exemplary embodiment;

FIG. 2 is a schematic view illustrating a brief configuration of theendoscope;

FIG. 3 is a view illustrating a camera head and a relay lens which arecoupled to each other;

FIG. 4A is a view illustrating a configuration component of an imagesensor;

FIG. 4B is a view illustrating an external configuration of the imagesensor;

FIG. 5 is a view illustrating a first structure example of a four colorseparation prism;

FIG. 6 a view illustrating a second structure example of the four colorseparation prism;

FIG. 7 is a graph illustrating an example of sensor sensitivity of theimage sensor;

FIG. 8 is a graph illustrating an example of spectroscopic properties ofthe four color separation prism;

FIG. 9 is a graph illustrating spectral sensitivity in a case where fourimage sensors are used;

FIG. 10 is a block diagram illustrating a configuration of an endoscopesystem according to the first exemplary embodiment;

FIG. 11 is a schematic view illustrating an image during a dual outputmode displayed on a display;

FIG. 12 a schematic view illustrating an image during a superposedoutput mode displayed on the display;

FIG. 13 is a graph illustrating spectral sensitivity of a three colorseparation prism according to a comparative example;

FIG. 14 is a view illustrating a structure example of a three colorseparation prism according to a second exemplary embodiment;

FIG. 15 is a block diagram illustrating a configuration example of anendoscope system according to the second exemplary embodiment;

FIG. 16 is a graph illustrating spectral sensitivity in a case wherethree image sensors are used and one of the image sensors receives IRand blue light;

FIG. 17 is a graph illustrating spectral sensitivity in a case where anIR and green color image sensor according to the comparative examplereceives IR light;

FIG. 18 is a view illustrating a structure example of a two colorseparation prism according to a third exemplary embodiment;

FIG. 19 is a block diagram illustrating a configuration example of anendoscope system according to the third exemplary embodiment;

FIG. 20 is a graph illustrating spectral sensitivity in a case where twoimage sensors are used; and

FIG. 21 is a graph illustrating spectral sensitivity of a three colorseparation prism according to the comparative example.

DETAILED DESCRIPTION Background of Exemplary Embodiment in PresentDisclosure

In surgery using an endoscope, an indocyamine green (ICG) which is afluorescent substance is administered into a body, and near infraredlight is emitted to an area such as an excessively accumulated tumor(affected area). The affected area is lightened so as to image an areaincluding the affected area in some cases. If the ICG is excited by thenear infrared light (for example, peak wavelength of 805 nm, 750 to 810nm), the ICG is a substance which fluoresces using the near infraredlight having a longer wavelength (for example, peak wavelength of 835nm).

In a case where a single board-type camera having one image sensoracquires an image of the affected area by receiving light containing anIR component, a filter for a red color (R) component, a green color (G)component, a blue color (B) component, and the IR component which aredivided into four is disposed on an incident surface of the imagesensor. Therefore, if a user tries to obtain desired colorreproducibility and resolution, a size of the image sensor has toincrease. Consequently, the single board-type camera is less likely tobe applied to the endoscope.

As illustrated in the endoscope system disclosed in Japanese PatentUnexamined Publication No. 2013-116357, in a case where a tripleboard-type camera using a three color separation prism acquires an imageof the affected area by receiving the light containing the IR component,signal strength of the IR component (for example, light having awavelength of 800 nm or greater) is weak as illustrated in FIG. 13.

FIG. 13 is a graph illustrating spectral sensitivity of the tripleboard-type camera according to a comparative example. In FIG. 13, avertical axis represents the spectral sensitivity, and a horizontal axisrepresents a wavelength. The spectral sensitivity corresponds to a ratiobetween a light quantity of light incident on each prism for theR-component, the G-component, and the B-component, and a light quantitydetected by an imaging element corresponding to each prism. Waveform h11represents the spectral sensitivity of the light having the R-component.Waveform h12 represents the spectral sensitivity of the light having theG-component. Waveform h13 represents the spectral sensitivity of thelight having the B-component. Waveform h11 also includes represents thespectral sensitivity of the light having the IR component.

As illustrated in FIG. 13, the image sensor which receives the lighthaving the R-component (refer to waveform h11) can acquire the lighthaving the IR component. In FIG. 13, the spectral sensitivity of the IRcomponent (for example, component having a wavelength of 800 nm orgreater) is lower than the spectral sensitivity of the light having theR-component, the G-component, and the B-component. If the signalstrength of the IR component is weak, an image (IR image) obtained bythe IR component is unclear. Accordingly, it is preferable to increasethe signal strength of the IR component so that the image (IR image)obtained by the IR component becomes clearer.

On the other hand, if the endoscope system disclosed in Japanese PatentUnexamined Publication No. 2013-116357 amplifies the IR component inorder to increase the signal strength of the IR component, the imageblurs or noise is emphasized on the image. Consequently, image qualityof the IR image becomes poor. Therefore, a desired area (affected area)containing the IR component is less likely to be observed from the imageobtained by the amplified IR component.

In a case of using the triple board-type camera, a blue color separationprism is normally disposed in the three color separation prism, as aprism on an object side on the light is incident. The reason is asfollows. The blue color component has a shorter wavelength than that ofthe red color component and the green color component. As the wavelengthbecomes shorter, the blue color component is less likely to receive theinfluence of polarized light.

In a case where a four color separation prism is disposed in theendoscope, the endoscope has a limited space for disposing the fourcolor separation prism. Accordingly, it is preferable to devise a methodof disposing a prism for each color (orientation for disposing the prismor angle relating to the prism).

Hereinafter, an endoscope and an endoscope system which can improveimage quality by adding an infrared light component to an image will bedescribed.

Hereinafter, exemplary embodiments will be described in detail withproper reference to the drawings. However, in some cases, unnecessarilydetailed description may be omitted. For example, in some cases,detailed description of well-known matters or repeated description ofsubstantially the same configuration may be omitted. The reason is toavoid the following description from becoming unnecessarily redundant,and to facilitate understanding of those skilled in the art. Theaccompanying drawings and the following description are provided inorder for those skilled in the art to fully understand the presentdisclosure. These are not intended to limit the gist disclosed in thescope of claims.

First Exemplary Embodiment

In a first exemplary embodiment, a quadruple board-type camera using afour color separation prism and four image sensors is disposed in acamera head of the endoscope. The four color separation prism separateslight focused by a relay lens into three primary color light of R-light(R-component), G-light (G-component), and B-light (B-component), and IRlight (IR component). For example, the IR component includes at least aportion of a wavelength band of 750 nm to 900 nm.

Configuration of Endoscope

FIG. 1 is a schematic view illustrating an external configuration ofendoscope 10 according to the first exemplary embodiment. FIG. 2 is aschematic view illustrating a brief configuration of endoscope 10.Endoscope 10 is a medical instrument which can be handled by a user withone hand. For example, endoscope 10 is configured to include scope 11,mount adapter 12, relay lens 13, camera head 14, operation switch 19,and light source connector 18.

For example, scope 11 is a main portion of a hard endoscope, which is tobe inserted into the body, and is an elongated light guide member whichcan guide light from a terminal end to a front end. Scope 11 has imagingwindow 11 z in the front end, and has an optical fiber through which anoptical image incident from imaging window 11 z is transmitted, and anoptical fiber which guides light L introduced from light sourceconnector 18 to the front end. As imaging window 11 z, optical materialssuch as optical glass and optical plastic are used.

Mount adapter 12 is a member for mounting scope 11 on camera head 14.Various scopes 11 can be mounted on mount adapter 12 so as to bedetachable therefrom.

Light source connector 18 introduces illumination light for illuminatingan area inside a body (affected area or the like) from a light sourcedevice (not illustrated). The illumination light includes visible lightand IR light. The light introduced to light source connector 18 isguided to the front end of scope 11 through scope 11, and is emitted tothe area inside the body (affected area or the like) from imaging window11 z. For example, the light source is an LED light source. Instead ofthe LED light source, the light source may be a xenon lamp or a halogenlamp.

Light source connector 18 is mounted on scope 11 via a connector betweenscope 11 and light source connector 18. The connector internally has amirror (not illustrated). The light guided from light source connector18 is reflected on the mirror, and is emitted to the affected area aftermoving forward to the front end side of scope 11.

Relay lens 13 focuses an optical image transmitted through scope 11 ontoan imaging surface. Relay lens 13 has one or more lenses. In accordancewith an operation amount of operation switch 19, relay lens 13 may movethe lens so as to perform focus adjustment and magnification adjustment.

Camera head 14 has a housing which can be gripped by a user (forexample, a doctor or an assistant) with a hand when in use (for example,during surgery), and internally has four color separation prism 20(refer to FIGS. 5 and 6), four image sensors 230, 231, 232, and 233(refer to FIGS. 5 and 6), and electronic board 250 (refer to FIG. 10).

Four color separation prism 20 is a quadruple board-type prism thatseparates light focused by relay lens 13 into three primary color lightof R-light (R-component), G-light (G-component), and B-light(B-component), and IR light (IR component). Four color separation prism20 is configured to include a light-transmitting member such as glass.

Image sensors 230 to 233 convert the optical image separated by fourcolor separation prism 20 and formed on each imaging surface into animage signal (electric signal).

As image sensors 230 to 233, an image sensor such as a charge coupleddevice (CCD) or complementary metal oxide semiconductor (CMOS) is used.

Four image sensors 230 to 233 are dedicated sensors which respectivelyreceive the light of the IR component, the B-component, the R-component,and the G-component. Therefore, unlike a single board-type camera whichreceives the light of the IR component, the R-component, theG-component, and the B-component by using a single image sensor, a smallsize image sensor can be employed as an individual image sensor. Forexample, an image sensor whose size is 1/2.86 inches is used.

For example, circuits including a signal output circuit for outputting asignal by using a low volt digital signal (LVDS) and a timing generator(TO) circuit (TO circuit) are mounted on electronic board 250 (simplyreferred to as a board) (refer to FIG. 10).

The signal output circuit outputs an RGB signal and an IR signal of animage captured by each of image sensors 230 to 233, as a pulse signal byusing the low volt digital signal (LVDS). The TG circuit supplies atiming signal (synchronizing signal) to each unit inside camera head 14.The RGB signal includes at least one of the R-component, theG-component, and the B-component. Without being limited to the RGBsignal, other color image signals (for example, HSV, YUV, YcCbCr, orYpbPr) may be output.

Signal cable 14 z for transmitting the image signal to camera controlunit (CCU) 30 (to be described later) is mounted on camera head 14.

FIG. 3 is a view illustrating camera head 14 and relay lens 13 which arecoupled to each other. An end surface of four color separation prism 20incorporated in camera head 14 is disposed so as to face flange surface13 v of relay lens 13.

Relay lens 13 forms an image on image sensors 230 to 233 inside camerahead 14 by using the light incident from a subject through scope 11mounted on mount adapter 12.

Relay lens 13 has focus ring 13 y and optical column 13 z. One endportion (lower end portion in the drawing) of relay lens 13 is mountedon a mounting target portion of mount adapter 12. The other end portion(upper end portion in the drawing) of relay lens 13 has screw-threadcutter 13 w having a predetermined height (for example, 4 mm).

Camera head 14 having four color separation prism 20 incorporatedtherein is screwed into screw-thread cutter 13 w, thereby mounting relaylens 13 on camera head 14. If relay lens 13 is mounted on camera head 14by screw-thread cutter 13 w, four color separation prism 20 insidecamera head 14 and the lens inside relay lens 13 face each other via agap. The gap prevents four color separation prism 20 and relay lens 13from coming into contact with each other.

If a distance of the gap is short, even if there is a limitation due toan optical path length of a C-mount (to be described later), four imagesensors 230 to 233 are likely to be disposed outside. On the other hand,if the distance of the gap is long, since there is the limitation due tothe optical path length of the C-mount, it becomes necessary to disposefour image sensors 230 to 233 inside (flange surface 13 v side of relaylens 13).

For example, camera head 14 and relay lens 13 are coupled to each otherin the C-mount. In the C-mount, in a state where relay lens 13 ismounted on camera head 14, a standard of an optical distance from flangesurface 13 v of relay lens 13 to the imaging surface of four imagesensors 230 to 233 is defined as L1=17.526 mm. In a case where aquadruple board-type camera (four color separation prism 20 and imagesensors 230 to 233) suitable for the optical path length of the C-mountis incorporated in camera head 14, the quadruple board-type camera isdisposed so as to have this optical path length.

The light which is guided from a subject by relay lens 13 through scope11 is focused by relay lens 13, thereby forming an image on four imagesensors 230 to 233 through four color separation prism 20 inside camerahead 14.

FIGS. 4A and 4B are views illustrating a configuration component and anexternal configuration of image sensor 230. Four image sensors 230 to233 have substantially the same specifications. Accordingly, theconfiguration will be described herein using IR image sensor 230.

As illustrated in FIGS. 4A and 4B, sensor element 230 y is accommodatedinside sensor package 230 w, and is fixed thereto using adhesive 230 v.Sensor package glass 230 x is disposed on a front surface of sensorpackage 230 w. Sensor element 230 y receives the light transmittedthrough sensor package glass 230 x. Sensor package 230 w is mounted onsensor board 230 z , and is molded as image sensor 230.

According to the present exemplary embodiment, as will be describedlater, image sensor 230 receives the IR light emitted from lightemission surface 220 c of IR separation prism (IR color separationprism) 220, and captures the IR image. Image sensors 231, 232, and 233for capturing a visible light image also have the same structure as thatof IR image sensor 230. A visible light cut filter for blocking lighthaving the wavelength of 700 nm or smaller is disposed on the frontsurface of IR image sensor 230. The visible light cut filter can improveimage quality of the IR image.

First Structure Example of Four Color Separation Prism

FIG. 5 is a view illustrating a first structure example (four colorseparation prism 20A) of four color separation prism 20. Four colorseparation prism 20A separates incident light guided by relay lens 13into the light of three primary color light of the R-component, theG-component, and the B-component, and the IR component. In four colorseparation prism 20A, IR separation prism 220, blue color separationprism 221, red color separation prism 222, and green color separationprism 223 are sequentially assembled in an optical axis direction. Thisarrangement order is an example, and other arrangement orders may beemployed. In FIG. 5, as will be described later, as an angle relating toa prism, θ1>θ2 is satisfied.

As illustrated in FIG. 5, in four color separation prism 20A, angle θ1formed between object side incident surface 220 a of IR separation prism220 and reflective surface 220 b of IR separation prism 220 is formed tobe greater than angle θ2 formed between an extension line of object sideincident surface 220 a of IR separation prism 220 and an extension lineof reflective surface 221 b of blue color separation prism 221. That is,θ1>θ2 is satisfied.

In other words, angle θ1 represents an angle formed between a straightline parallel to object side incident surface 220 a of IR separationprism 220 and a straight line parallel to reflective surface 220 b. Inother words, angle θ2 represents an angle formed between the straightline parallel to object side incident surface 220 a of IR separationprism 220 and a straight line parallel to reflective surface 221 b ofblue color separation prism 221.

IR image sensor 230 is disposed so as to face light emission surface 220c of IR separation prism 220. Blue color image sensor 231 is disposed soas to face light emission surface 221 c of blue color separation prism221. Red color image sensor 232 is disposed so as to face light emissionsurface 222 c of red color separation prism 222. Green color imagesensor 233 is disposed so as to face light emission surface 223 c ofgreen color separation prism 223.

For example, image sensors 230 to 233 are CCD or CMOS image sensorsincluding respective pixels which are arrayed in a horizontal (H)direction and a vertical (V) direction. Image sensors 230 to 233 convertthe optical image in which the light separated into each color of IR, R,G, and B forms an image on each imaging surface, into an electricsignal.

In IR separation prism 220, the incident light is incident on objectside incident surface 220 a of IR separation prism 220. The lightreflected on reflective surface 220 b facing object side incidentsurface 220 a is totally reflected at a boundary of object side incidentsurface 220 a of IR separation prism 220, and is incident on IR imagesensor 230 after being emitted from light emission surface 220 c facingobject side incident surface 220 a. For example, IR reflective film 240is formed on reflective surface 220 b by vapor deposition. IR separationprism 220 causes the light of the IR component in the incident light tobe reflected thereon, and causes other light (light of the B-component,the R-component, and the G-component) to be transmitted therethrough. IRimage sensor 230 causes the light reflected on reflective surface 220 band object side incident surface 220 a to be incident thereon, therebyreceiving the light. In this way, IR separation prism 220 is molded sothat the light moves forward in IR separation prism 220.

In blue color separation prism 221, the light (incident light)transmitted through IR separation prism 220 is incident on object sideincident surface 221 a of blue color separation prism 221. The lightreflected on reflective surface 221 b facing object side incidentsurface 221 a is totally reflected at a boundary of object side incidentsurface 221 a of blue color separation prism 221, and is incident onblue color image sensor 231 after being emitted from light emissionsurface 221 c facing object side incident surface 221 a. For example,blue light reflective film 241 is formed on reflective surface 221 b byvapor deposition. Blue color separation prism 221 causes the light ofthe B-component in the incident light to be reflected thereon, andcauses other light (light of the R-component and the G-component) to betransmitted therethrough. Blue color image sensor 231 causes the lightreflected on reflective surface 221 b and object side incident surface221 a to be incident thereon, thereby receiving the light. In this way,blue color separation prism 221 is molded so that the light movesforward in blue color separation prism 221.

In red color separation prism 222, the light (incident light)transmitted through blue color separation prism 221 is incident onobject side incident surface 222 a of red color separation prism 222.The light reflected on reflective surface 222 b facing object sideincident surface 222 a is totally reflected at a boundary of object sideincident surface 222 a of red color separation prism 222, and isincident on red color image sensor 232 after being emitted from lightemission surface 222 c facing object side incident surface 222 a. Forexample, red light reflective film 242 is formed on reflective surface222 b by vapor deposition. Red color separation prism 222 causes thelight of the R-component in the incident light to be reflected thereon,and causes other light (light of the G-component) to be transmittedtherethrough. Red color image sensor 232 causes the light reflected onreflective surface 222 b and object side incident surface 222 a to beincident thereon, thereby receiving the light. In this way, red colorseparation prism 222 is molded so that the light moves forward in redcolor separation prism 222.

In green color separation prism 223, the light (incident light)transmitted through red color separation prism 222 is incident on objectside incident surface 223 a of green color separation prism 223, and isincident on green color image sensor 233 after being emitted from lightemission surface 223 c facing object side incident surface 223 a. Inthis way, green color separation prism 223 is molded so that the lightmoves forward in green color separation prism 223.

The number of light reflected times in each color separation prism isnormally an even number of times (for example, twice, 0 times). Thereason is that mirror image information is output from the colorseparation prism in a case where the number of reflected times is an oddnumber of times.

Consideration on Shape and Layout Relationship of Color Separation Prism

Next, a shape and a layout relationship of each color separation prismin four color separation prism 20A will be considered.

In four color separation prism 20A, IR separation prism 220 and IR imagesensor 230, and blue color separation prism 221 and blue color imagesensor 231 are disposed on opposite sides across incident light centerline ILC. Incident light center line ILC represents an optical path ofthe light in a plurality of incident rays which are vertically incidenton object side incident surface 220 a of IR separation prism 220. Thelight is transmitted through IR separation prism 220, is transmittedthrough blue color separation prism 221, is transmitted through redcolor separation prism 222, is incident on center C1 (refer to FIG. 4B)on a light receiving surface of green color image sensor 233 facinglight emission surface 233 c of green color separation prism 223. Here,IR image sensor 230 is disposed on an upper side (refer to FIG. 5) fromincident light center line ILC, and blue color image sensor 231 isdisposed on a lower side (refer to FIG. 5) from incident light centerline ILC.

Red color separation prism 222 and red color image sensor 232 arearranged between blue color separation prism 221 and blue color imagesensor 231, and green color separation prism 223 and green color imagesensor 233.

Here, red color separation prism 222 and red color image sensor 232 aredisposed on the lower side from incident light center line ILC, in viewof a layout space inside camera head 14 (refer to FIG. 5). If the layoutposition of red color image sensor 232 is disposed on the upper sidefrom incident light center line ILC, due to a limited space insidecamera head 14, the layout position of red color image sensor 232overlaps the layout position of IR image sensor 230 or the layoutposition of green color separation prism 223. Accordingly, it becomesdifficult to physically dispose these sensors.

Since red color image sensor 232 is disposed on the lower side fromincident light center line ILC, endoscope 10 enables four colorseparation prism 20A to be disposed inside the limited layout space.Therefore, it is possible to miniaturize camera head 14 whichaccommodates the four color separation prism.

In FIG. 5, IR separation prism 220 is disposed to be closest to theobject side among the respective color separation prisms. That is, IRseparation prism 220 is disposed closer to the object side than othercolor separation prisms (blue color separation prism 221, red colorseparation prism 222, and green color separation prism 223) whenreceiving the light incident from the affected area.

In this manner, IR image sensor 230 disposed to face light emissionsurface 220 c of IR separation prism 220 can receive the IR light asmuch as possible. The IR light fluoresces with lower light intensitycompared to the light of the B-component, the R-component, and theG-component. That is, with regard to the light incident on four colorseparation prism 20A, four color separation prism 20A can restrain alight quantity of the IR component received by IR image sensor 230 fromdecreasing due to prism transmission. Four color separation prism 20Acan acquire a clearly captured image of the affected area, based onfluorescence generated by the light of the IR component being emitted toa fluorescent substance (for example, ICG) inside the affected area.

In FIG. 5, blue color separation prism 221 is disposed closer to theobject side, subsequently (secondly) to IR separation prism 220. Thereason is that the B-component has a shorter wavelength than that of theR-component and the G-component. As the wavelength becomes shorter, eachcolor separation prism receives less influence of polarized light whichcan occur when the light is reflected. Therefore, since in four colorseparation prism 20A, blue color separation prism 221 is disposed closerto the object side than red color separation prism 222 and green colorseparation prism 223, it is possible to restrain the influence of thepolarized light.

Blue color separation prism 221 is disposed closer to the object sidethan IR separation prism 220. In this case, in view of the spectroscopicproperties of blue light reflective film 241 used for blue colorseparation prism 221, spectral transmittance becomes higher on a highwavelength side (that is, the green color component side and the redcolor component side) in FIG. 8. Accordingly, a reflected amount of theIR light increases in blue light reflective film 241, thereby decreasingthe light quantity of the IR light incident on IR separation prism 220disposed in the rear stage.

Therefore, in endoscope 10, since IR separation prism 220 is disposedcloser to the object side than blue color separation prism 221 asillustrated in FIG. 5, an image obtained by the IR light can have higherimage quality compared to a case where blue color separation prism 221is disposed closer to the object side than IR separation prism 220. Thatis, based on the fluorescence of the ICG, endoscope 10 can acquire animage which clearly shows a state of the affected area.

Green color separation prism 223 and green color image sensor 233 aredisposed so as to receive the light by setting incident light centerline ILC as substantially the center. In this manner, without a need todispose a green light reflective film, it is possible to simplify ashape of green color separation prism 223. Accordingly, it is possibleto easily design a configuration element relating to the G-component.

It is preferable that the order of green color separation prism 223 isthe last to receive the incident light. That is, is preferable thatgreen color separation prism 223 is disposed farthest from the objectside among a plurality of color separation prisms. The G-component isincluded in an intermediate wavelength band between the B-component andthe R-component. In a front stage from green color separation prism 223,IR reflective film 240, blue light reflective film 241, and red lightreflective film 242 can easily block light components other than theG-component. These reflective films can be designed as a low pass filter(LPF) or a high pass filter (HPF). Accordingly, it is possible to easilydesign filters.

Second Structure Example of Four Color Separation Prism

FIG. 6 a view illustrating a second structure example (four colorseparation prism 20B) of four color separation prism 20. In four colorseparation prism 20B, description of the same structure as that of fourcolor separation prism 20A illustrated in FIG. 5 will be omitted orsimplified.

Compared to four color separation prism 20A described above, four colorseparation prism 20B satisfies θ2>θ1. Since angles are different fromeach other in this way, each color separation prism has a mutuallydifferent shape, orientation, and size. Through detailed considerationof the present inventor, it is found that a case of θ2=θ1 also adoptsthe same configuration as that of four color separation prism Billustrated in FIG. 6.

IR image sensor 230 causes the light reflected on reflective surface 220b and object side incident surface 220 a to be incident thereon, therebyreceiving the light. Angle θ1 illustrated in FIG. 6 is smaller thanangle θ1 illustrated in FIG. 5. Accordingly, a reflective angle (angleformed between a line perpendicular to reflective surface 220 b and alight ray reflected from reflective surface 220 b) on reflective surface220 b of IR separation prism 220 becomes smaller than that in a caseillustrated in FIG. 5. Similarly, a reflective angle (angle formedbetween a line perpendicular to object side incident surface 220 a and alight ray reflected from object side incident surface 220 a) on objectside incident surface 220 a also becomes smaller than that in the caseillustrated in FIG. 5.

Therefore, an orientation of the light ray reflected on object sideincident surface 220 a is close to an orientation of the light raymoving forward in green color separation prism 223, and a position of IRimage sensor 230 is close to a position of green color image sensor 233.

In order to secure a required optical path length, IR separation prism220 is designed so that a distance between object side incident surface220 a and light emission surface 220 c is longer than that in a caseillustrated in FIG. 5. Accordingly, reflective surface 220 b of IRseparation prism 220 is bent along the light ray reflected on objectside incident surface 220 a, and thus, a shape of IR separation prism220 is complicated. Reflective surface 220 b requires polishing in orderto transmit the light components other than the IR component. However,if reflective surface 220 b is bent, reflective surface 220 b is lesslikely to be polished.

In this way, a front end portion of IR separation prism 220 (end portionincluding light emission surface 220 c and IR image sensor 230) isformed close to green color separation prism 223 side. Accordingly,compared to the case illustrated in FIG. 5, it becomes more difficult todispose red color separation prism 222 between the front end portion ofIR separation prism 220 and green color separation prism 223. Therefore,red color separation prism 222 together with blue color separation prism221 is disposed on the lower side from incident light center line ILC.

Blue color image sensor 231 causes the light reflected on reflectivesurface 221 b and object side incident surface 221 a to be incidentthereon, thereby receiving the light. Angle θ2 illustrated in FIG. 6 islarger than angle θ2 illustrated in FIG. 5. Accordingly, a reflectiveangle (angle formed between a line perpendicular to reflective surface221 b and a light ray reflected from reflective surface 221 b) onreflective surface 221 b of blue color separation prism 221 becomeslarger than that in the case illustrated in FIG. 5. Similarly, areflective angle (angle formed between a line perpendicular to objectside incident surface 221 a and a light ray reflected from object sideincident surface 221 a) on object side incident surface 221 a alsobecomes larger than that in the case illustrated in FIG. 5.

Therefore, the light reflected on object side incident surface 221 a andemitted from light emission surface 221 c is close to the incidentsurface of four color separation prism 20B (that is, object sideincident surface 220 a of IR separation prism 220), and is received inan end portion on object side incident surface 220 a in blue color imagesensor 231.

Design is made so as to satisfy the following condition. The lightreflected on reflective surface 221 b of blue color separation prism 221does not go beyond a range of object side incident surface 221 a, and isreflected on object side incident surface 221 a. The light is totallyreflected on object side incident surface 221 a.

Next, pixel addition will be described.

IR image sensor 230 may output an electric signal having each pixelvalue (signal level) without any change. However, IR image sensor 230may output the electric signal having a pixel value subjected to H/Vpixel addition processing by performing the H/V pixel additionprocessing for adding pixel values of pixels adjacent in a horizontal(H) or vertical (V) direction.

If H/V pixels are added, for example, in a case where the pixel value ofIR image sensor 230 is approximately “30”, the pixel value of the IRcomponent becomes “120” (=30×4) by adding the pixels.

If it is assumed that the pixel value of the IR component in the relatedart is approximately “10”, IR image sensor 230 is independently disposedaccording to endoscope 10 of the present exemplary embodiment.Accordingly, compared to a case in the related art, the pixel value ofthe IR component can be obtained as much as approximately 3 times to 12times.

It is assumed that the pixel value of respective RGB image sensors 231,232, and 233 according to the present exemplary embodiment isapproximately “100”. In this case, if the H/V pixel addition processingis added, each signal level of the R-component, the G-component, and theB-component becomes substantially the same as a signal level of the IRcomponent. Accordingly, the RGB image and the IR image are likely to bevisible. The RGB image is obtained using at least one signal of theR-component, the G-component, and the B-component. The IR image isobtained using the signal of the IR component.

Sensor Sensitivity of Image Sensor

FIG. 7 is a graph illustrating sensor sensitivity of image sensor 230.The vertical axis represents the sensor sensitivity. The sensorsensitivity corresponds to a ratio of the light quantity detected byimage sensor 230 with respect to the light quantity of the lightincident on image sensor 230. The sensor sensitivity illustrated in FIG.7 is an absolute value in a case where the sensor sensitivity in thelight wavelength of 510 nm is set to value 1. The horizontal axisrepresents the light wavelength in units of nm. Waveform gh1 representsproperties of the sensor sensitivity of image sensor 230 according tothe present exemplary embodiment with respect to the light wavelength.Waveform gh2 represents properties of the sensor sensitivity of an imagesensor according to a comparative example (in the related art) withrespect to the light wavelength.

In a case of image sensor 230 according to the present exemplaryembodiment, as illustrated by waveform gh1, the sensor sensitivity inthe light wavelength of 830 nm is value 0.551, which is approximately55% compared to a case of the light wavelength of 510 nm. On the otherhand, in a case of the image sensor according to the comparativeexample, as illustrated by waveform gh2, the sensor sensitivity in thelight wavelength of 830 nm is value 0.298, which is approximately 30%compared to the case of the light wavelength of 510 nm. The wavelengthband of 830 nm is the wavelength band of the fluorescence using the ICG.

Compared to the sensor sensitivity of the image sensor according to thecomparative example, the sensor sensitivity of image sensor 230according to the present exemplary embodiment is substantially the samesensitivity in a blue light region (B-component) of 400 nm to 500 nm.However, the sensor sensitivity of image sensor 230 becomes higher in agreen light region (G-component) of 500 nm to 600 nm and a red lightregion (R-component) of 600 nm to 700 nm. Furthermore, compared to thesensor sensitivity of the image sensor according to the comparativeexample, the sensor sensitivity of image sensor 230 is high even in anear infrared light (IR light) region (IR component) of 750 nm to 900nm.

Hereinafter, an image sensor having the properties of the sensorsensitivity illustrated by waveform gh1 is referred to as a highsensitivity sensor. An image sensor having the properties of the sensorsensitivity illustrated by waveform gh2 is referred to as a normalsensitivity sensor. As can be understood from FIG. 7, the highsensitivity sensor has high sensitivity on the long wavelength side,compared to the normal sensitivity sensor.

In the first exemplary embodiment, the high sensitivity sensor is usedfor image sensors 230 to 233. Although the high sensitivity sensor isused for red color, green color, and blue color image sensors 231 to233, the normal sensitivity sensor may be used.

Spectroscopic Properties of Four Color Separation Prism

FIG. 8 is a graph illustrating an example of spectroscopic properties(spectral transmittance) of four color separation prism 20. The verticalaxis in FIG. 8 represents each spectral transmittance (%), andcorresponds to a ratio of the light quantity of the light incident onimage sensors 230 to 233 in each prism with respect to the lightquantity of the light incident on each prism. The horizontal axis inFIG. 8 represents the wavelength (nm) of the light incident onrespective image sensors 230 to 233. The light quantity of the lightincident on image sensors 230 to 233 in each prism corresponds to thelight quantity of the light emitted from each prism.

In FIG. 8, waveform h1 (solid line) illustrates the spectroscopicproperties of the light of the IR component which is incident on IRimage sensor 230. Transmittance of the light of the IR component whichis incident on IR image sensor 230 in the light incident on four colorseparation prism 20 has a peak waveform whose wavelength is near 900 nmin the wavelength of 800 to 1,000 nm and whose transmittance isapproximately 70%.

Waveform h2 (one-dot chain line) illustrates the spectroscopicproperties of the light of the R-component which is incident on redcolor image sensor 232. Transmittance of the light of the R-componentwhich is incident on red color image sensor 232 has a peak waveformwhose wavelength is near 600 nm and whose transmittance is approximately80%.

Waveform h3 (dotted line) illustrates the spectroscopic properties ofthe light of the B-component which is incident on blue color imagesensor 231. Transmittance of the light of the B-component which isincident on blue color image sensor 231 has a peak waveform whosewavelength is near 450 nm and whose transmittance exceeds 60%.

Waveform h4 (two-dot chain line) illustrates the spectroscopicproperties of the light of the G-component which is incident on greencolor image sensor 233. Transmittance of the light of the G-componentwhich is incident on green color image sensor 233 has a peak waveformwhose wavelength is near 530 nm and whose transmittance is approximately90%.

In this way, any transmittance of the light of the IR component, theR-component, the B-component, and the G-component which are separated byfour color separation prism 20 exceeds 60%. Therefore, each pixel valueof the IR component, the R-component, the B-component, and theG-component can be suitably obtained, and a signal of the IR componentmay not be greatly amplified. In this manner, in a case where theaffected area is imaged, color reproducibility of a captured imageincluding the IR component is improved.

Spectral Sensitivity of Quadruple Board-type Camera

FIG. 9 is a graph illustrating the spectral sensitivity in a case wherefour image sensors 230 to 233 are used. The vertical axis in FIG. 9represents the spectral sensitivity in units of percentage. Thehorizontal axis in FIG. 9 represents a wavelength (nm) of the lightincident on respective image sensors 230 to 233. The spectralsensitivity corresponds to the light quantity of the light having eachwavelength detected by image sensors 230 to 233 with respect to thelight quantity of the light incident on four color separation prism 20.The spectral sensitivity is obtained in such a way that the sensorsensitivity illustrated in FIG. 7 is multiplied by the spectraltransmittance illustrated in FIG. 8. The spectral sensitivity is one ofperformance indicators of the quadruple board-type camera inside camerahead 14. In FIG. 9, the maximum value of the sensor sensitivity of thenormal sensitivity sensor illustrated by waveform gh6 in FIG. 7 (sensorsensitivity in a case where the wavelength is 510 nm in both the normalsensitivity sensor and the high sensitivity sensor) is set to value 1.In this manner, value 1 is multiplied by the spectral transmittance offour color separation prism 20. Therefore, the spectral sensitivity of100% indicates a state where the spectral transmittance of four colorseparation prism 20 is 100% and the sensor sensitivity of the normalsensitivity sensor is the maximum.

The spectral sensitivity illustrated in FIG. 9 has each high value in ablue light region, a green light region, a red light region, and a nearinfrared light region, when the light passes through four colorseparation prism 20.

Here, a peak value of the spectral sensitivity in the green light region(wavelength band including 530 nm) is approximately 90% (refer towaveform br2). On the other hand, a peak value of the spectralsensitivity in the near infrared light region (wavelength band including830 nm) is approximately 48%, and has a value equal to or greater than40% of the peak value (90%) of the spectral sensitivity in the greenlight region (530 nm) (refer to waveform bra Therefore, the spectralsensitivity in the IR region is obtained so as to have a desired highvalue. Here, the peak value of the spectral sensitivity in the greenlight region corresponds to the maximum value of the spectralsensitivity in all of the wavelength bands including the visible lightband of the RGB. Although not illustrated, in the related art, the peakvalue of the spectral sensitivity in the near infrared light region isapproximately half (approximately 24%) of the spectral sensitivity ofthe quadruple board-type camera according to the present exemplaryembodiment.

In this way, the quadruple board-type camera included in camera head 14has a peak value of 40% equal to or greater than a peak value in thevisible light region (here, a peak value in the green light region).That is, the quadruple board-type camera has high sensitivity for the IRlight.

The sensor sensitivity of the image sensors illustrated in FIGS. 7 to 9,the spectroscopic properties of four color separation prism 20, and thespectral sensitivity of the quadruple board-type camera are examples,the endoscope system may have other properties.

Configuration of Endoscope System

FIG. 10 is a block diagram illustrating a configuration of endoscopesystem 5 according to the first exemplary embodiment. Endoscope system 5is configured to include endoscope 10, CCU 30, and display 40. CCU 30 isan example of a processor. Display 40 is an example of a display device.Camera head 14 of endoscope 10 has four color separation prism 20, andimage sensors 230, 231, 232, and 233 which are described above. In FIG.10, camera head 14 further has respective element drivers 141 i, 141 r,141 b, and 141 g, drive signal generator 142, synchronizing signalgenerator 143, and signal output 145.

Element driver 141 i drives image sensor 230 in accordance with a drivesignal. Element driver 141 r drives image sensor 231 in accordance witha drive signal. Element driver 141 b drives image sensor 232 inaccordance with a drive signal. Element driver 141 g drives image sensor233 in accordance with a drive signal.

Drive signal generator 142 generates the drive signal for respectiveelement drivers 141 i, 141 r, 141 b, and 141 g. Synchronizing signalgenerator 143 corresponds to a function of a timing generator (TG)circuit, and supplies a synchronizing signal (timing signal) to drivesignal generator 142.

Signal output 145 transmits an electric signal output from image sensors230, 231, 232, and 233 to CCU 30 via signal cable 14 z by using an LVDSmethod, for example. Signal output 145 may transmit a synchronizingsignal output from synchronizing signal generator 143 to CCU 30 viasignal cable 14 z. Signal output 145 may transmit an operation signal ofoperation switch 19 to CCU 30 via signal cable 14 z. Signal output 145corresponds to a function of a signal output circuit.

CCU 30 fulfills various functions by executing a program stored in aninternal or external memory (not illustrated) of CCU 30. The variousfunctions include each function of RGB signal processor 22, IR signalprocessor 23, and output 28.

RGB signal processor 22 converts the electric signals of theB-component, the R-component, and the G-component which are output fromimage sensors 231, 232, and 233, into video signals which can bedisplayed on display 40, and outputs the video signals to output 28.

IR signal processor 23 converts the electric signal of the IR componentoutput from image sensor 230 into a video signal, and outputs the videosignal to output 28. IR signal processor 23 may have gain adjuster 23 z.Gain adjuster 23 z adjusts an amplification degree (gain) when theelectric signal of the IR component which is output from IR image sensor230 is converted into the video signal. For example, gain adjuster 23 zmay adjust signal strength of the video signal of the RGB component soas to be substantially the same as signal strength of the video signalof the IR component.

Gain adjuster 23 z enables a user to reproduce the IR image for the RGBimage with optional intensity. Instead of adjusting the amplificationdegree of the electric signal of the IR component, or in conjunctionwith the adjustment, RGB signal processor 22 may adjust theamplification degree of the electric signal of the RGB component.

When signal processing is performed, RGB signal processor 22 and IRsignal processor 23 receives the synchronizing signal output fromsynchronizing signal generator 143, and are operated in accordance withthe synchronizing signal. In this manner, an image (video image) of eachRGB color component and an image of the IR component are adjusted so asnot to cause a time lag.

In accordance with the synchronizing signal output from synchronizingsignal generator 143, output 28 outputs at least any one of the videosignal of each RGB color component and the video signal of the IRcomponent, to display 40. For example, output 28 outputs the videosignal, based on any one of a dual output mode and a superposed outputmode.

During the dual output mode, output 28 simultaneously outputs RGB imageG1 and IR image G2 (refer to FIG. 11) using different screens. The dualoutput mode enables a user to observe the affected area tg by comparingthe RGB image and the IR image with each other using the differentscreens.

During the superposed output mode, output 28 outputs synthesized imageGZ in which the RGB image and the IR image are superposed on each other(refer to FIG. 12). For example, the superposed output mode enables auser to clearly observe affected area tg which fluoresces due to the ICGand the IR light serving as illumination light inside the RGB image.

An example has been described in which RGB signal processor 22, IRsignal processor 23, and output 28 perform processing using software bythe processor inside CCU 30 cooperating with the memory. However, all ofthese may be configured to respectively include dedicated hardware.

Based on the video signal output from CCU 30, display 40 causes a screento display an image of an object such as affected area tg which isimaged by endoscope 10 and which is output from CCU 30. In a case of thedual output mode, display 40 divides the screen into a plurality ofscreens (for example, into two screens), and causes each screen todisplay RGB image G1 and IR image G2 side by side (refer to FIG. 11). Ina case of the superposed output mode, display 40 causes one screen todisplay synthesized image GZ in which RGB image G1 and IR image G2 aresuperposed on each other (refer to FIG. 12).

In this way, in endoscope system 5, in a case where an area inside abody is imaged using endoscope 10, an indocyamine green (ICG) which is afluorescent substance may be administered into the body, and nearinfrared light may be emitted to an area such as an excessivelyaccumulated tumor (affected area). The affected area may be lightened soas to image the affected area.

Light L which is introduced into light source connector 18 by a useroperating operation switch 19 is guided to a front end side of scope 11,and is emitted from imaging window 11 z, thereby illuminating an areaaround the affected area which includes the affected area. The lightreflected on the affected area and the like is guided to a rear end sideof scope 11 through imaging window 11 z, is focused by relay lens 13,and is incident on four color separation prism 20 of camera head 14.

In four color separation prism 20, the light of the IR componentseparated by IR separation prism 220 in the incident light forms animage as an optical image of the infrared light component in IR imagesensor 230. The light of the B-component separated by blue colorseparation prism 221 forms an image as an optical image of the bluecolor component in blue color image sensor 231. The light of theR-component separated by red color separation prism 222 forms an imageas an optical image of the red color component in red color image sensor232. The light of the G-component separated by green color separationprism 223 forms an image as an optical image of the green colorcomponent in green color image sensor 233.

The electric signal of the IR component which is converted by IR imagesensor 230 is converted into the video signal by IR signal processor 23inside CCU 30, and is output to output 28. Each electric signal of theB-component, the R-component, and the G-component which are respectivelyconverted by visible light image sensors 231, 232, and 233 are convertedinto each video signal by RGB signal processor 22 inside CCU 30, and isoutput to output 28. The video signal of the IR component and therespective video signals of the B-component, the R-component, and theG-component are synchronized with each other, and are output to display40.

In a case where output 28 sets the dual output mode, display 40 causestwo screen to simultaneously display RGB image G1 and IR image G2. FIG.11 is a schematic view illustrating an image during the dual output modedisplayed on display 40. RGB image G1 is a color image by imaging thearea including affected area tg after emitting the visible lightthereto. IR image G2 is a black and white image (any optional color canbe set) by imaging the area including affected area tg after emittingthe IR light thereto.

In a case where output 28 sets the superposed output mode, display 40displays synthesized image GZ1 in which RGB image G1 and IR image G2 aresuperposed on (synthesized with) each other. FIG. 12 a schematic viewillustrating an image during the superposed output mode displayed ondisplay 40.

Advantageous Effect

In this way, endoscope 10 according to the present exemplary embodimentincludes four color separation prism 20 that includes the first colorseparation prism, the second color separation prism, the third colorseparation prism, and the fourth color separation prism whichrespectively separate the light reflected from the affected area intothe first color component, the second color component, the third colorcomponent, and the fourth color component which are any one of the bluecolor component, the red color component, the green color component, andthe IR component, the first color image sensor that is installed in thefirst color separation prism, and that converts the separated firstcolor component into the electric signal, the second color image sensorthat is installed in the second color separation prism, and thatconverts the separated second color component into the electric signal,the third color image sensor that is installed in the third colorseparation prism, and that converts the separated third color componentinto the electric signal, the fourth color image sensor that isinstalled in the fourth color separation prism, and that converts theseparated fourth color component into the electric signal, and signaloutput 145 that outputs the color image signal and the IR signal fromthe respective converted electric signals. The first color separationprism, the second color separation prism, the third color separationprism, and the fourth color separation prism are sequentially disposedfrom the object side when receiving the light incident from the affectedarea. The first color image sensor is disposed opposite to the secondcolor image sensor and the third color image sensor across the incidentray which is incident vertically to the object side incident surface ofthe first color separation prism. For example, the incident ray isincident light center line ILC.

In this manner, endoscope 10 can usefully and efficiently dispose eachcolor separation prism (particularly, the third color separation prism),and can easily realize four color separation prism 20. For example, dueto the layout position of the first color separation prism and the firstcolor image sensor, the layout space for the third color separationprism is small on the upper side of the incident ray (one region withrespect to the incident ray). However, the layout space can be securedon the lower side of the center line of the incident ray (the otherregion with respect to the incident ray). Accordingly, four colorseparation prism 20 can be mounted on endoscope 10, and each independentimage sensor can receive each color component separated by each colorseparation prism. Therefore, the light strength of each color componentis likely to be secured. Accordingly, although the light emitting amountis small in the fluorescence, endoscope 10 improves image quality byadding the infrared light component to the image. Endoscope 10 canadjust color balance by independently controlling each color component,and can improve color reproducibility of each color component.

Second Exemplary Embodiment

In the first exemplary embodiment, the quadruple board-type prism hasbeen described. In a second exemplary embodiment, a triple board-typeprism will be described which separates the light into the IR light andthree of the B-light, R-light, and G-light. That is, camera head 14includes a three color separation prism and three image sensors. The IRlight is separated using the blue color separation prism, and isreceived by the image sensor.

In the present exemplary embodiment, the same reference numerals will begiven to the same matters as those in the first exemplary embodiment,and description thereof will be omitted or simplified.

FIG. 14 is a view illustrating a structure example of three colorseparation prism 20A according to the second exemplary embodiment. Threecolor separation prism 20A separates the incident light guided by relaylens 13 into the R-light, G-light, B-light, and IR light. In three colorseparation prism 20A, IR and blue color separation prism 320, red colorseparation prism 321, and green color separation prism 322 aresequentially assembled in the optical axis direction.

IR and blue color image sensor 330 is disposed to face light emissionsurface 320 c of IR and blue color separation prism 320. Red color imagesensor 331 is disposed to face light emission surface 321 c of red colorseparation prism 321. Green color image sensor 332 is disposed to facelight emission surface 322 c of green color separation prism 322.

For example, image sensors 330 to 332 are CCD or CMOS image sensorsincluding respective pixels which are arrayed in a horizontal (H)direction and a vertical (V) direction. Image sensors 330 to 332 convertthe optical image in which the light separated into each color of IR, B,R, and G forms an image on each imaging surface, into the electricsignal. The IR light is detected by IR and blue color image sensor 330,and thus, the IR light glows in a blue color.

In IR and the blue color separation prism 320, the incident light isincident on incident surface 320 a of IR and the blue color separationprism 320. The light reflected on reflective surface 320 b facingincident surface 320 a is totally reflected at a boundary of incidentsurface 320 a of IR and blue color separation prism 320, and is incidenton IR and blue color image sensor 330 after being emitted from lightemission surface 320 c facing incident surface 320 a. For example, IRand blue light reflective film 340 is formed on reflective surface 320 bby vapor deposition. IR and blue color separation prism 320 causes thelight of the IR and blue color component in the incident light to bereflected thereon, and causes other light (light of the R-component andthe G-component) to be transmitted therethrough. IR and blue color imagesensor 330 causes the light reflected on reflective surface 320 b andincident surface 320 a to be incident thereon, thereby receiving thelight. In this way, IR and blue color separation prism 320 is molded sothat the light moves forward in IR and blue color separation prism 320.

In red color separation prism 321, the light (incident light)transmitted through IR and blue color separation prism 320 is incidenton incident surface 321 a of red color separation prism 321. The lightreflected on reflective surface 321 b facing incident surface 321 a istotally reflected at a boundary of incident surface 321 a of red colorseparation prism 321, and is incident on red color image sensor 331after being emitted from light emission surface 321 c facing incidentsurface 321 a. For example, red light reflective film 341 is formed onreflective surface 321 b by vapor deposition. Red color separation prism321 causes the light of the R-component in the incident light to bereflected thereon, and causes other light (light of the G-component) tobe transmitted therethrough. Red color image sensor 331 causes the lightreflected on reflective surface 321 b and incident surface 321 a to beincident thereon, thereby receiving the light. In this way, red colorseparation prism 321 is molded so that the light moves forward in redcolor separation prism 321.

In green color separation prism 322, the light (incident light)transmitted through red color separation prism 321 is incident onincident surface 322 a of green color separation prism 322, and isincident on green color image sensor 332 after being emitted from lightemission surface 322 c facing incident surface 322 a. In this way, greencolor separation prism 322 is molded so that the light moves forward ingreen color separation prism 322.

In the triple board-type camera (three color separation prism 20A andimage sensors 330 to 332), an optical distance (optical path length)from flange surface 13 v of relay lens 13 to image sensors 330 to 332 isset to 17.526 mm in a case of the C-mount. A refractive index of threecolor separation prism 20A may be the same value as “1.8” which is arefractive index of four color separation prism 20. In a case of thetriple board-type camera, there is more room in the layout spacecompared to the quadruple board-type camera. Accordingly, the refractiveindex of three color separation prism 20A may be a value of therefractive index which is slightly smaller than that of the quadrupleboard-type camera, for example, “1.7”. Compared to the quadrupleboard-type camera, the refractive index is lowered to a slightly smallervalue. In this manner, an actual distance (length) of the tripleboard-type camera is shortened.

FIG. 15 is a block diagram illustrating a configuration example ofendoscope system 5A according to the second exemplary embodiment. Theendoscope system according to the second exemplary embodiment hassubstantially the same configuration as that according to the firstexemplary embodiment. The same reference numerals will be given to thesame configuration elements as those according to the first exemplaryembodiment, and description thereof will be omitted or simplified. Here,a configuration and an operation which are different from thoseaccording to the first exemplary embodiment will be mainly described.

According to the second exemplary embodiment, unlike the first exemplaryembodiment, three element driver 241 ib, element driver 241 r, andelement driver 241 g are mounted on electronic board 250.

Element driver 241 ib drives IR and blue color image sensor 330 inaccordance with a drive signal. Element driver 241 r drives red colorimage sensor 331 in accordance with a drive signal. Element driver 241 gdrives green color image sensor 332 in accordance with a drive signal.

Drive signal generator 142 generates the drive signals for each ofelement drivers 241 ib, 241 r, and 241 g.

Signal output 145 transmits the electric signal output from imagesensors 330, 331, and 332 to CCU 30A. According to the present exemplaryembodiment, unlike the first exemplary embodiment, signal output 145transmits the signal of the R-component (R-signal), the signal of theG-component (G-signal) and the signal (BIR signal) including at leastone of the B-component and the IR component, to CCU 30A.

Instead of RGB signal processor 22 and IR signal processor 23, CCU 30Aincludes R-signal processor 261 for converting the R-signal into a videosignal, G-signal processor 262 for converting the G-signal into a videosignal, and BIR signal processor 263 for converting the BIR signal intoa video signal. BIR signal processor 263 includes gain adjuster 23 z.CCU 30A is the same as CCU 30 except for a configuration and anoperation of the signal processor.

FIG. 16 is a graph illustrating spectral sensitivity in a case wherethree image sensors 330, 331, and 332 are used and one image sensor 330receives the IR and blue color light. The vertical axis in FIG. 16represents the spectral sensitivity in units of percentage. Thehorizontal axis in FIG. 16 represents a wavelength (nm) of the lightincident on respective image sensors 330 to 332. The spectralsensitivity corresponds to the light quantity of the light having eachwavelength detected by image sensors 330 to 332 with respect to thelight quantity of the light incident on three color separation prism20A. The spectral sensitivity is obtained in such a way that the sensorsensitivity illustrated in FIG. 6 is multiplied by the spectraltransmittance of three color separation prism 20A. Although notillustrated, the spectral transmittance of three color separation prism20A is the same as the spectral transmittance of four color separationprism 20 according to the first exemplary embodiment, for example. Thespectral sensitivity is one of performance indicators of the tripleboard-type camera inside camera head 14.

IR and blue color image sensor 330 receives the light in the blue lightregion and the IR light through IR and the blue color separation prism320. As IR and blue color image sensor 330, the high sensitivity sensorillustrated in the first exemplary embodiment is used. As red colorimage sensor 331 and green color image sensor 332, the high sensitivitysensor may be used, or the normal sensitivity sensor may be used.

FIG. 16 illustrates the spectral sensitivity (refer to waveform br3) ina case of using the high sensitivity sensor and the spectral sensitivity(refer to waveform br4) in a case of using the normal sensitivitysensor. Since endoscope 10 uses the high sensitivity sensor, thespectral sensitivity in the IR region can be improved.

In the graph illustrated in FIG. 16, a peak value of the spectralsensitivity near the wavelength of 580 nm in the green light regionwhich is received by green color image sensor 332 is approximately 94%.On the other hand, a peak value of the spectral sensitivity near thewavelength of 830 nm in the IR region is approximately 40%. Therefore,the peak value of the spectral sensitivity in the IR region isapproximately 42.5% (40%/94%) of the peak value of the spectralsensitivity in the visible light region (here, the wavelength of 580nm), that is, 40% or greater. In this manner, the spectral sensitivityin the IR region can be obtained as a desired high value.

Here, as an comparative example, a case will be described where thegreen color image sensor receives the IR light.

FIG. 17 is a graph illustrating spectral sensitivity in a case where IRand green color image sensor 332 x (not illustrated) receives the IRlight, as the comparative example. IR and green color image sensor 332 xreceives the light in the green light region and the IR light throughgreen color separation prism 322 x. In the graph of the sensorsensitivity illustrated in FIG. 17, the sensor sensitivity of the highsensitivity sensor in the green light region (500 nm to 600 nm) becomeshigher than that of the normal sensitivity sensor.

In the green light region, compared to the spectral sensitivity of thenormal sensitivity sensor illustrated by waveform gr2 in FIG. 17, thespectral sensitivity of the high sensitivity sensor illustrated bywaveform gr1 becomes higher. Therefore, in a case where IR and greencolor image sensor 332 x is used, the light receiving sensitivity of theIR light can be improved. On the other hand, the color balance in thevisible light region is disturbed, and the color reproducibility(distribution of the RGB color component) becomes poor.

In the graph illustrated in FIG. 17, the peak value of the spectralsensitivity of the wavelength of 580 nm in the green light region isapproximately 105%. On the other hand, the peak value of the spectralsensitivity of the wavelength of 830 nm in the IR region isapproximately 40%. That is, the peak value of the spectral sensitivityin the IR region is approximately 38% (40%105%) of the peak value of thespectral sensitivity in the green light region, that is, smaller than40%. Therefore, as the spectral sensitivity in the IR region, it isdifficult to obtain a desired value.

If the red color image sensor receives the IR light, there is a highpossibility of an unsuitable configuration due to the following reason.The wavelength band (for example, the wavelength band of 680 nm) of theexcitation light used for fluorescence may be in the red light region,or mat red color components as the color component are present insidethe living body.

According to endoscope 10 of the second exemplary embodiment, the sensorsensitivity of IR and blue color image sensor 330 is that of the highsensitivity sensor. Therefore, compared to the sensor sensitivity of thenormal sensitivity sensor, IR and blue color image sensor 330 has acharacteristic which is highly sensitive on the long wavelength in theIR light region. Accordingly, endoscope 10 can improve the spectralsensitivity of the IR light, compared to the spectral sensitivity of theRGB light in the visible light region.

As illustrated in FIG. 16, in the blue light region, the sensorsensitivity of the high sensitivity sensor is approximately the same asthe sensor sensitivity of the normal sensitivity sensor. Therefore, evenif the normal sensitivity sensor is replaced with the high sensitivitysensor, endoscope 10 can restrain the color balance from being disturbedin the visible light region.

In this way, in endoscope 10, the color separation prism may includethree color separation prism 20A which separates the light incident fromthe object into three color components of the red color component, thegreen color component, and the blue color component and the infraredlight component. The image sensor may include three image sensors 330 to332 which respectively convert the optical image of the three separatedcolor components into the electric signals.

In this manner, even in a case where three color separation prism 20A isused, endoscope 10 can improve the spectral sensitivity in thewavelength region of the infrared light, compared to the spectralsensitivity in the wavelength region of the three primary color light inthe visible light region. Accordingly, for example, in a case where theaffected area is imaged using the ICG, the fluorescing affected area iseasily visible using the IR image by restraining a change in the RGBimage showing the entire area including the affected area.

Endoscope 10 causes one image sensor to detect the blue color componentand the infrared light component. In this manner, even if the highsensitivity sensor is used as the image sensor, endoscope 10 can improvethe spectral sensitivity of the infrared light component by reducing achange in the spectral sensitivity of the blue color component.Therefore, visibility of the infrared light component can be improved byrestraining poor color reproducibility (change in distribution of eachcolor component) of each color component of three primary colors.

Third Exemplary Embodiment

The first exemplary embodiment employs the quadruple board-type prism,and the second exemplary embodiment employs the triple board-type prism.However, in a third exemplary embodiment, a case of employing a doubleboard-type prism for separating the light into the IR light and the RGBlight will be described.

In the present exemplary embodiment, the same reference numerals will begiven to the same matters as those in the first exemplary embodiment orthe second exemplary embodiment, and description thereof will be omittedor simplified.

FIG. 18 is a view illustrating a structure example of two colorseparation prism 20B according to the third exemplary embodiment. Twocolor separation prism 20B separates the incident light guided by relaylens 13 into the light of the RGB component which is the light of thethree primary color light, and the light of the IR component. In twocolor separation prism 20B, IR separation prism 420 and RGB colorseparation prism 421 are sequentially assembled in the optical axisdirection.

IR image sensor 430 is disposed to face light emission surface 420 c ofIR separation prism 420. RGB color image sensor 431 is disposed to facelight emission surface 421 c of RGB color separation prism 421.

For example, image sensors 430 and 431 are CCD or CMOS image sensorsincluding respective pixels which are arrayed in the horizontal (H)direction and the vertical (V) direction. Image sensors 430 and 431convert the optical image in which the light separated into two colorsof the IR and the RGB colors forms an image on each imaging surface,into the electric signal.

In IR separation prism 420, the incident light is incident on incidentsurface 420 a of IR separation prism 420. The light reflected onreflective surface 420 b facing incident surface 420 a is totallyreflected at a boundary of incident surface 420 a of IR separation prism420, and is incident on IR image sensor 430 after being emitted fromlight emission surface 420 c facing incident surface 420 a. For example,IR reflective film 440 is formed on reflective surface 420 b by vapordeposition. IR separation prism 420 causes the IR light in the incidentlight to be reflected thereon, and causes other light (light of the RGBcomponent) to be transmitted therethrough. IR image sensor 430 causesthe light reflected on reflective surface 420 b and incident surface 420a to be incident thereon, thereby receiving the light. In this way, IRseparation prism 420 is molded so that the light moves forward in IRseparation prism 420.

In RGB color separation prism 421, the light (incident light)transmitted through IR separation prism 420 is incident on incidentsurface 421 a of RGB color separation prism 421, and is incident on RGBimage sensor 431 after being emitted from light emission surface 421 cfacing incident surface 421 a. In this way, RGB color separation prism421 is molded so that the light moves forward in RGB color separationprism 421.

In the double board-type camera (two color separation prism 20B andimage sensors 430 and 431), in a case of the C-mount, the opticaldistance (optical path length) from flange surface 13 v of relay lens 13to image sensors 430 and 431 is also set to 17.526 mm. The refractiveindex of two color separation prism 20B may be the same as “1.8” whichis the refractive index of four color separation prism 20. In a case ofthe double board-type camera, there is more room in the layout space,compared to the quadruple board-type camera. Accordingly, the refractiveindex of two color separation prism 20B may be a smaller refractiveindex value than that of the quadruple board-type camera or the tripleboard-type camera, for example, “1.7” or smaller than “1.7”. Compared tothe quadruple board-type camera or the triple board-type camera, therefractive index has the smaller value. Accordingly, the actual distance(length) of the double board-type camera is shortened.

FIG. 19 is a block diagram illustrating a configuration example ofendoscope system 5B according to the third exemplary embodiment. Theendoscope system according to the third exemplary embodiment hassubstantially the same configuration as that according to the first orsecond exemplary embodiment. The same reference numerals will be givento the same configuration elements as those according to the first orsecond exemplary embodiment, and description thereof will be omitted orsimplified. Here, a configuration and an operation which are differentfrom those according to the first or second exemplary embodiment will bedescribed.

Unlike the first exemplary embodiment, according to the third exemplaryembodiment, two element driver 341 i and element driver 341 c aremounted on electronic board 250.

Element driver 341 i drives IR image sensor 430 in accordance with adrive signal. Element driver 341 c drives RGB image sensor 431 inaccordance with a drive signal.

Drive signal generator 142 generates the drive signals for each ofelement drivers 341 i and 341 c.

Signal output 145 transmits the electric signal output from imagesensors 430 and 431 to CCU 30. A configuration and an operation of CCU30 are the same as those according to the first exemplary embodiment,and CCU 30 processes the IR signal and the RGB signal.

FIG. 20 is a graph illustrating spectral sensitivity in a case where twoimage sensors 430 and 431 are used. The vertical axis in FIG. 20represents the spectral sensitivity in units of percentage. Thehorizontal axis in FIG. 20 represents a wavelength (nm) of the lightincident on respective image sensors 430 and 431. The spectralsensitivity corresponds to the light quantity of the light having eachwavelength detected by image sensors 430 and 431 with respect to thelight quantity of the light incident on two color separation prism 20B.The spectral sensitivity is obtained in such a way that the sensorsensitivity illustrated in FIG. 6 is multiplied by the spectraltransmittance of two color separation prism 20B. Although notillustrated, the spectral transmittance of two color separation prism20B is the same as the spectral transmittance of three color separationprism 20A according to the second exemplary embodiment or the spectraltransmittance of four color separation prism 20 according to the firstexemplary embodiment, for example. The spectral sensitivity is one ofperformance indicators of the double board-type camera inside camerahead 14.

IR image sensor 430 receives the IR light through IR separation prism420. As IR image sensor 430, the high sensitivity sensor illustrated inthe first exemplary embodiment is used. As RGB image sensor 431, thehigh sensitivity sensor may be used, or the normal sensitivity sensormay be used.

In the graph illustrated in FIG. 20, a peak value of the spectralsensitivity near the wavelength of 600 nm in the red light region isapproximately 100%. On the other hand, a peak value of the spectralsensitivity near the wavelength of 860 nm in the IR region isapproximately 47%. Therefore, the peak value of the spectral sensitivityin the IR region is approximately 47% (47%/100%) of the peak value ofthe spectral sensitivity of the wavelength of 600 nm, that is, 47% orgreater. Therefore, the spectral sensitivity in the IR region isobtained so as to have a desired high value.

According to endoscope 10 of the third exemplary embodiment, the sensorsensitivity of IR light image sensor 430 is that of the high sensitivitysensor. Therefore, compared to the sensor sensitivity of the normalsensitivity sensor, IR and blue color image sensor 330 has acharacteristic which is highly sensitive on the long wavelength in theIR light region. Accordingly, endoscope 10 can improve the spectralsensitivity of the IR light, compared to the spectral sensitivity of theRGB light in the visible light region.

Since the double board-type camera is used, compared to the quadrupleboard-type camera or the triple board-type camera, the layout space hasmore room, and thus, the actual length can be lengthened. Therefore, therefractive index of the prism can be lowered. In this case, it ispossible to reduce the cost required for the prism in endoscope 10. Inendoscope 10, a size of camera head 14 can be miniaturized bymaintaining a state where the actual length of the double board-typecamera is short.

In this way, in endoscope 10, the color separation prism may include twocolor separation prism 20B which separates the light incident from theobject into two color components of the three primary color light andthe infrared light. The image sensor may include two image sensors 430and 431 which respectively convert the optical image of the twoseparated color components into the electric signals.

In this manner, even in a case where two color separation prism 20B isused, endoscope 10 can improve the spectral sensitivity in thewavelength region of the infrared light, compared to the spectralsensitivity in the wavelength region of the three primary color light inthe visible light region. Accordingly, for example, in a case where theaffected area is imaged using the ICG, the fluorescing affected area iseasily visible using the IR image by restraining a change in the RGBimage showing the entire area including the affected area.

Hitherto, various exemplary embodiments have been described withreference to the drawings. However, as a matter of course, the presentinvention is not limited by the examples. Those skilled in the art willappreciate that various modification examples or correction examples areconceivable within the scope described in claims. As a matter of course,it is obvious that those examples belong to the technical scope of thepresent invention.

For example, in the above-described exemplary embodiments, an examplehas been described in which a rigid endoscope is employed as endoscope10. However, a rigid endoscope having another configuration may beemployed, or a soft endoscope may be employed. The configuration or theoperation of endoscope 10 may be applied to an optical microscope. Relaylens 13 and camera head 14 comply with the standards of the C-mount,thereby improving versatility. Accordingly, the above-describedexemplary embodiments can be easily applied to the optical microscope.

In the above-described exemplary embodiments, an example has beendescribed in which the ICG is administered into the living body as anoptical contrast agent. However, any other optical contrast agentinstead of the ICG may be administered. In this case, in accordance withthe wavelength of the excitation light for exciting the optical contrastagent, the spectroscopic properties or the spectral sensitivity in thewavelength region of the invisible light may be determined.

In the above-described exemplary embodiments, a chemical whichfluoresces in the wavelength region of the infrared light is used.However, a chemical which fluoresces in the wavelength region ofultraviolet light may be used. Even in this case, similarly to a casewhere the optical contrast agent which fluoresces in the near infraredlight region, the endoscope can capture an image of the affected areawhich fluoresces.

In the above-described exemplary embodiments, an example has been mainlydescribed in which relay lens 13 and camera head 14 comply with thestandards of the C-mount. However, both of these may not comply with thestandards of the C-mount.

In the above-described exemplary embodiments, a configuration ofreference numeral 13 may be the mount adapter. Alternatively, aconfiguration may be adopted in which the mount adapter internally hasthe relay lens.

In the above-described exemplary embodiments, CCU 30 has been describedas an example of the processor. As long as the processor controlsendoscope system 5, the processor may adopt any physical configuration.Therefore, the processor is not limited to CCU 30. However, ifprogrammable CCU 30 is used, processing content can be changed bychanging the program. Accordingly, the processor can be more freelydesigned. The processor may be configured to include one semiconductorchip, or may be configured to physically include a plurality ofsemiconductor chips. In a case where the processor is configured toinclude the plurality of semiconductor chips, each control in the firstexemplary embodiment may be realized by each different semiconductorchip. In this case, it is conceivable that the plurality ofsemiconductor chips configure one processor. The processor may beconfigured to include a member (capacitor or the like) having a functionwhich is different from that of the semiconductor chip. Onesemiconductor chip may be configured so as to realize a functionbelonging to the processor and other functions. As long as aprogrammable circuit is used, with regard to the circuit mounted onelectronic board 250, the processing content can be changed by changingthe program. The number of circuits may be one or more.

1. A medical camera, comprising: a camera head including: a first colorseparation prism, a second color separation prism, a third colorseparation prism, and a fourth color separation prism which respectivelyseparate light incident from an affected area into a first colorcomponent, a second color component, a third color component, and afourth color component which are any one of a blue color component, ared color component, a green color component, and an infrared (IR)component, wherein a light emission surface of the first colorseparation prism is disposed opposite to a light emission surface of thesecond color separation prism and a light emission surface of the thirdcolor separation prism is disposed across an incident ray, which isincident vertically to an object side incident surface of the firstcolor separation prism.
 2. The medical camera of claim 1, wherein afirst angle formed between the object side incident surface of the firstcolor separation prism and a reflective surface of the first colorseparation prism is greater than a second angle formed between theobject side incident surface of the first color separation prism and areflective surface of the second color separation prism.
 3. The medicalcamera of claim 1, wherein a boundary between the first color separationprism and the second color separation prism includes the reflectivesurface of the first color separation prism on a first side of theboundary, and an object side incident surface of the second colorseparation prism on a second side of the boundary.
 4. The medical cameraof claim 1, wherein a boundary between the second color separation prismand the third color separation prism includes the reflective surface ofthe second color separation prism on a first side of the boundary, andan object side incident surface of the third color separation prism on asecond side of the boundary.
 5. The medical camera of claim 1, wherein aboundary between the third color separation prism and the fourth colorseparation prism includes the reflective surface of the third colorseparation prism on a first side of the boundary, and an object sideincident surface of the fourth color separation prism on a second sideof the boundary.
 6. The medical camera of claim 3, wherein the boundaryis at an angle with respect to the object side incident surface of thefirst color separation prism.
 7. The medical camera of claim 4, whereinthe boundary is at an angle with respect to the object side incidentsurface of the first color separation prism.
 8. The medical camera ofclaim 5, wherein the boundary is at an angle with respect to the objectside incident surface of the first color separation prism.
 9. Themedical camera of claim 1, wherein the first color separation prism isdisposed to be closest to an object side among the first colorseparation prism, the second color separation prism, the third colorseparation prism and the fourth color separation prism.
 10. The medicalcamera of claim 9, wherein the first color separation prism is disposedto transmit more IR light amount than the second color separation prism,the third color separation prism or the fourth color separation prism.11. The medical camera of claim 1, wherein the first color separationprism is configured such that the incident ray is transmitted throughthe object side incident surface of the first color separation prismwhile a portion of the transmitted incident ray hits a reflectivesurface of the first color separation prism and is reflected at an angletowards the object side incident surface of the first color separationprism, and the reflected portion of the incident ray hits the objectside incident surface of the first color separation prism and isreflected again at an angle towards an exit of the first colorseparation prism.
 12. The medical camera of claim 1, wherein the secondcolor separation prism is configured such that a portion of the incidentray is transmitted through an object side incident surface of the secondcolor separation prism while a portion of the transmitted incident rayhits the reflective surface of the second color separation prism and isreflected at an angle towards the object side incident surface of thesecond color separation prism, and the reflected portion of the incidentray hits the object side incident surface of the second color separationprism and is reflected again at an angle towards an exit of the secondcolor separation prism.
 13. The medical camera of claim 1, wherein thethird color separation prism is configured such that a portion of theincident ray is transmitted through an object side incident surface ofthe third color separation prism while a portion of the transmittedincident ray hits the reflective surface of the third color separationprism and is reflected at an angle towards the object side incidentsurface of the third color separation prism, and the reflected portionof the incident ray hits the object side incident surface of the thirdcolor separation prism and is reflected again at an angle towards anexit of the third color separation prism.
 14. The medical camera ofclaim 1, wherein the camera head is configured to output an image in twomodes, the two modes including a dual output mode that simultaneouslyoutputs a color image and an IR image to be displayed as two separateimages, and a superposed mode that synthesizes the color image and theIR image and outputs a synthesized image.
 15. The medical camera ofclaim 14, wherein the color image includes a combination of the bluecolor component, the red color component, and the green color component.16. The medical camera of claim 1, wherein the camera head is connectedto a display configured to receive one or more images captured by thecamera head.
 17. The medical camera of claim 1, wherein the camera headprocesses the first color component, the second color component, thethird color component, and the fourth color component to generate an RGBsignal and an IR signal, and simultaneously outputs, to a display, theRGB signal and the IR signal.
 18. The medical camera of claim 1, whereinthe camera head synthesizes the first color component, the second colorcomponent, the third color component, and the fourth color component togenerate a synthesized image and outputs, to a display, the synthesizedimage.
 19. An endoscope comprising: the medical camera of claim
 1. 20. Amicroscope comprising: the medical camera of claim 1.